It’s because it was taken with a time exposure late at night. The camera was placed on a tripod in Palau, Sardinia, Italy where I lived off ship and the camera lens was opened for a minute or so to allow it to slowly gather La Maddalena city light reflected from the clouds until the water and some other details were visible. You could’t actually see this scene with the naked eye in the darkness.

Determining the proper exposure time was simply a matter of taking several different exposures for something like 15 seconds, 30 seconds, 60 seconds, etc. so that one would turn out to be ideal.